audioflinger: avoid cross deadlock with when releasing effect

There is a possible cross deadlock between EffectModule mutexes in
AudioFlinger and AudioPolicyService mutex when destroying an
EffectHandle in audio flinger.

This change reduces this likelyhood of this happening but does not
fix the root cause.

Bug: 180941720
Test: make.
Change-Id: Ib2cd04869143c9146accee468cc5d40f65c373b9